Sonochemical Deposition of Palladium Nanoparticles Onto the Surface of N-Doped Carbon Nanotubes: A Simplified One-Step Catalyst Production Method

Highly efficient mobility, separation and charge transfer in black SnO2-TiO2 structures with co-catalysts: the key step for the photocatalytic hydrogen evolution

Oxygen vacancies and co-catalysts enhance photocatalytic hydrogen production by improving the charge carrier separation. Herein, the black SnO2-TiO2 structure (BST) was synthesized for the first time by two consecutive methods. First, the sol-gel nucleation method allowed TiO2 to form on the SnO2 nanoparticles, creating a strong interaction and direct contact between them. Subsequently, this structure was reduced by NaBH4 during thermal treatment, generating (Ti3+/Sn2+) states to form the BST. Then, 2 wt% of Co, Cu or Pd was impregnated onto BST. The results showed that the activity raised with the presence of Ti3+/Sn2+ states, reaching a hydrogen generation rate of 147.50 μmol g-1 h-1 with BST in comparison with the rate of 99.50 μmol g-1 h-1 for white SnO2-TiO2. On the other hand, the interaction of the co-catalysts with the BST structure helped to increase the photocatalytic hydrogen production rates: 154.10 μmol g-1 h-1, 384.18 μmol g-1 h-1 and 480.20 μmol g-1 h-1 for cobalt-BST, copper-BST and palladium-BST, respectively. The results can be associated with the creation of Ti3+/Sn2+ at the BST interface that changes the lifetime of the charge carrier, improving the separation of photogenerated electrons and holes and the co-catalysts in the structures move the flat band position and increasing the photocurrent response to having electrons with greater reducing power.

Solvated electron-induced synthesis of cyclodextrin-coated Pd nanoparticles: mechanistic, catalytic, and anticancer studies

Herein, using in situ generated solvated electrons in the reaction media, a highly time-efficient, one-pot green approach has been employed to synthesize palladium (Pd) nanoparticles (NPs) coated with a molecular assembly of α-cyclodextrin (α-CD). The appearance of a shoulder peak at 280 nm in the UV-Vis absorption spectra indicated the formation of Pd NPs, which was further confirmed from their cubic phase XRD pattern. The nanomorphology varied considerably as a function of the dose rate, wherein sphere-shaped NPs (average size ∼ 7.6 nm) were formed in the case of high dose rate electron-beam assisted synthesis, while nanoflakes self-assembled to form nanoflower-shaped morphologies in a γ-ray mediated approach involving a low dose rate. The formation kinetics of NPs was investigated by pulse radiolysis which revealed the formation of Pd-based transients by the solvated electron-induced reaction. Importantly, no interference of α-CD was observed in the kinetics of the transient species, rather it played the role of a morphology directing agent in addition to a biocompatible stabilizing agent. The catalytic studies revealed that the morphology of the NPs has a significant effect on the reduction efficiency of 4-nitrophenol to 4-aminophenol. Another important highlight of this work is the demonstration of the morphology-dependent anticancer efficacy of Pd NPs against lung and brain cancer cells. Notably, flower-shaped Pd NPs exhibited significantly higher cancer cell killing as compared to spherical NPs, while being less toxic towards normal lung fibroblasts. Nonetheless, these findings show the promising potential of Pd NPs in anticancer treatment.

Pyrene Functionalized Highly Reduced Graphene Oxide-palladium Nanocomposite: A Novel Catalyst for the Mizoroki-Heck Reaction in Water

The formation of a C-C bond through Mizoroki-Heck cross-coupling reactions in water with efficient heterogeneous catalysts is a challenging task. In this current study, a highly reduced graphene oxide (HRG) immobilized palladium (Pd) nanoparticle based catalyst (HRG-Py-Pd) is used to catalyze Mizoroki-Heck cross-coupling reactions in water. During the preparation of the catalyst, amino pyrene is used as a smart functionalizing ligand, which offered chemically specific binding sites for the effective and homogeneous nucleation of Pd NPs on the surface of HRG, which significantly enhanced the physical stability and dispersibility of the resulting catalyst in an aqueous medium. Microscopic analysis of the catalyst revealed a uniform distribution of ultrafine Pd NPs on a solid support. The catalytic properties of HRG-Py-Pd are tested towards the Mizoroki-Heck cross-coupling reactions of various aryl halides with acrylic acid in an aqueous medium. Furthermore, the catalytic efficacy of HRG-Py-Pd is also compared with its non-functionalized counterparts such as HRG-Pd and pristine Pd NPs (Pd-NPs). Using the HRG-Py-Pd nanocatalyst, the highest conversion of 99% is achieved in the coupling reaction of 4-bromoanisol and acrylic acid in an aqueous solution in a relatively short period of time (3 h), with less quantity of catalyst (3 mg). Comparatively, pristine Pd NPs delivered lower conversion (∼92%) for the same reaction required a long reaction time and a large amount of catalyst (5.3 mg). Indeed, the conversion of the reaction further decreased to just 40% when 3 mg of Pd-NPs was used which was sufficient to produce 99% conversion in the case of HRG-Py-Pd. On the other hand, HRG-Pd did not deliver any conversion and was ineffective even after using a high amount of catalyst and a longer reaction time. The inability of the HRG-Pd to promote coupling reactions can be attributed to the agglomeration of Pd NPs which reduced the dispersion quality of the catalyst in water. Therefore, the high aqueous stability of HRG-Py-Pd due to smart functionalization can be utilized to perform other organic transformations in water which was otherwise not possible.

Precious-Metal-Decorated Chromium(IV) Oxide Nanowires as Efficient Catalysts for 2,4-Toluenediamine Synthesis

The catalytic hydrogenation of 2,4-dinitrotoluene (DNT) to 2,4-toluenediamine (TDA) is a key step in the production of polyurethanes; therefore, the development of efficient hydrogenation catalysts for industrial use is of paramount importance. In the present study, chromium(IV) oxide nanowires were decorated by palladium and platinum nanoparticles in a one-step, simple, and fast preparation method to yield highly efficient hydrogenation catalysts for immediate use. The nanoparticles were deposited onto the surface of CrO2 nanowires by using ultrasonic cavitation and ethanol as a reduction agent. Beneficially, the catalyst became catalytically active right at the end of the preparation and no further treatment was necessary. The activity of the Pd- and Pt-decorated CrO2 catalysts were compared in the hydrogenation of 2,4-dinitrotoluene (DNT). Both catalysts have shown high activity in the hydrogenation tests. The DNT conversion exceeded 98% in both cases, whereas the 2,4-toluenediamine (TDA) yields were 99.7 n/n% and 98.8 n/n%, with the Pd/CrO2 and Pt/CrO2, respectively, at 333 K and 20 bar H2 pressure. In the case of the Pt/CrO2 catalyst, 304.08 mol of TDA formed with 1 mol Pt after 1 h hydrogenation. Activation energies were also calculated to be approximately 24 kJ∙mol-1. Besides their immediate applicability, our catalysts were well dispersible in the reaction medium (methanolic solution of DNT). Moreover, because of their magnetic behavior, the catalysts were easy to handle and remove from the reaction media by using a magnetic field.